In a mobile radio system operating according to the TDMA principle, data information is transmitted between a base station and one or more mobiles (mobile stations), with the data information containing call and other information such as synchronising, fault correction etc.
As mentioned, transmission takes place over a given radio channel, e.g. within the frequency range of 935-960 MHz in the form of frames, each containing a given number of time slots. The data information consists of a bit flow having a given rate e.g. 340 kbits/s, and between the different mobiles in the form of bursts corresponding to the time slots in a frame. Accordingly, a mobile is usually alloted a time slot in a frame during which the bursts are transmitted or received. A plurality of mobiles can thus transmit or receive over a given radio channel, i.e. radio frequency range.
The cellular system can be divided into large and small cells, where the small cells usually serve mobiles in a densely populated area, while the large cells serve sparsely populated areas. In spite of this, it is often the case that all time slots in a frame for mobiles within the small cells are occupied, whereas one or more of the time slots for the mobiles within the large cells are not occupied.